1. Field of the Invention
The present invention relates to a liquid crystal drive circuit (source drive circuit and gate drive circuit or the like) which drives a matrix line group (gate line group and source line group or the like) placed in a liquid crystal panel of a liquid crystal device (liquid crystal display).
This application is counterpart of Japanese patent application, Serial Number 164786/2003, filed Jun. 10, 2003, the subject matter of which is incorporated herein by reference.
2. Description of the Related Art
As a conventional liquid crystal drive circuit, there has been proposed one wherein high-speed liquid crystal driving is realized by a precharge operation which upon 1-dot inversion driving or plural-dot inversion driving, disconnects output terminals (matrix lines) of the liquid drive circuit from outputs of drivers thereof and short-circuits the same to a common power supply or other output terminals disconnected from their corresponding drivers in like manner (see, for example, Japanese Laid Open Patent Application JP-A-11-30975.
FIG. 14 is a configurational diagram of such a conventional liquid crystal display. The conventional liquid crystal display includes a liquid crystal panel 1, a gate drive circuit 2, a source drive circuit 3, a source line group (m source lines S1 through Sm) and a gate line group (n gate lines G1 through Gn).
FIG. 15 is a circuit configurational diagram showing the conventional source drive circuit 3. As shown in FIGS. 14 and 15, the conventional source drive circuit 3 includes a source driver group (m source drivers SD1 through SDm), an analog switch group A (m analog switches A1 through Am) an analog switch group B (m analog switches B1 through Bm) and an inverter I.
In the conventional source drive circuit 3, the analog switch group A is turned OFF and the analog switch B is turned ON when an input signal PC is “0 and an output signal PCB of the inverter I is “1”. Thus, output terminals OUT1 through OUTm (source lines S1 through Sm) of the source drive circuit 3 are connected to their corresponding outputs of the source drivers SD1 through SDm so that signals outputted from the source drivers SD1 through SDm are respectively outputted to the source lines S1 through Sm.
Then, when the input signal PCB is brought to “1” and the output signal PCB of the inverter I reaches “0”, the analog switch group A is turned ON and the analog switch group B is turned OFF so that the output terminals OUT1 through OUTm (source lines S1 through Sm) of the source drive circuit 3 are respectively disconnected from the outputs of the source drivers SD1 through SDm. Thus, the output terminals OUT1 through OUTm thereof are short-circuited to a common power supply Vcom so that precharge is carried out.
When the input signal PC is returned to “0” and the output signal PCB of the inverter I is returned to “1”, the analog switch group A is turned OFF and the analog switch group B is turned ON so that the output terminals OUT1 through OUTm (source line S1 through Sm) of the source drive circuit 3 are disconnected from the common power supply Vcom and connected to the outputs of the source drivers SD1 through SDm again, respectively.
In the conventional liquid crystal drive circuit, however, the two analog switch groups are controlled by the same one input signal PC. Therefore, a delay is developed in switching timing between both analog switch groups due to the capacitance of each analog switch and wiring capacitance or the like. The analog switches of the other analog switch group might be turned ON before the analog switches of one analog switch group are perfectly turned OFF.
In such a case, a problem arises in that the matrix lines are short-circuited before they are respectively disconnected from the outputs of the drivers, or the matrix lines are respectively connected to the outputs of the drivers before the short circuit of the matrix lines are cut off, whereby the outputs of the drivers are instantaneously short-circuited to cause a flow of overcurrent, thus no obtaining the original effect of the precharge operation.